[bug]: Invalid parameters to updatechanpolicy --create_missing_edge makes the channel permanently unfixable

[jogc]

Pre-Submission Checklist

• I have searched the existing issues and believe this is a new bug.
• I am not asking a question about how to use lnd, but reporting a bug (otherwise open a discussion).

LND Version

v0.20.1

LND Configuration

(Nothing relevant)

Backend Version

Bitcoin Core

Backend Configuration

(Nothing relevant)

OS/Distribution

Debian x86

Bug Details & Steps to Reproduce

When using updatechanpolicy --create_missing_edge you only get one chance to get it right. You have to specify all the values for the updatechanpolicy and it's not apparent what all of them are supposed to be. So if you for example put a too big value for max_htlc_msat so you get something like this back:

{
    "failed_updates": [
        {
            "outpoint": "X:x",
            "reason": "UPDATE_FAILURE_INVALID_PARAMETER",
            "update_error": "max htlc size of X mSAT is above max pending amount of X mSAT"
        }
    ]
}

you are screwed. updatechanpolicy has now put the channel edge in some kind of irrecoverable state that is not fixable. But if you get everything right immediately it does manage to recreate the edge.

Full example:

We accidently put a too big value for max_htlc_msat:

lncli updatechanpolicy --create_missing_edge --min_htlc_msat=X --max_htlc_msat=X X X X X:x
{
    "failed_updates": [
        {
            "outpoint": "X:x",
            "reason": "UPDATE_FAILURE_INVALID_PARAMETER",
            "update_error": "max htlc size of X mSAT is above max pending amount of X mSAT"
        }
    ]
}

We try again with a valid value:

lncli updatechanpolicy --create_missing_edge --min_htlc_msat=X --max_htlc_msat=X X X X X:x
{
    "failed_updates": [
        {
            "outpoint": "X:x",
            "reason": "UPDATE_FAILURE_UNKNOWN",
            "update_error": "could not add edge"
        }
    ]
}

We try once again with the same values just because why not:

lncli updatechanpolicy --create_missing_edge --min_htlc_msat=X --max_htlc_msat=X X X X X:x
{
    "failed_updates": [
        {
            "outpoint": "X:x",
            "reason": "UPDATE_FAILURE_NOT_FOUND",
            "update_error": "edge policy not found"
        }
    ]
}

The channel is now unfixable and further tries will give the same error:

{
    "failed_updates": [
        {
            "outpoint": "X:x",
            "reason": "UPDATE_FAILURE_NOT_FOUND",
            "update_error": "edge policy not found"
        }
    ]
}

More context: #10567

Possibly related waiting PR: #10516

Expected Behavior

For updatechanpolicy to either fix the channel or to give an error message but not touch (modify) the database at all

Debug Information

No response

Environment

No response

[github-actions]

Found 1 possible duplicate issue:

1. Graph data for local channels sometimes missing #10447

If this issue is a duplicate, please close it and 👍 the existing issue instead.

🤖 Generated with Claude Code

[lightninglabs-deploy]

Consolidating related issues here. The following have been closed as duplicates:

• [bug]: updatechanpolicy error: "channel from self node has no policy" #7247 — Reports the same "channel from self node has no policy" error when calling updatechanpolicy on testnet (lnd v0.15.5-beta). Minimal reproduction: simply run lncli updatechanpolicy --base_fee_msat 0 --fee_rate_ppm 50 --time_lock_delta 69. No additional log output.
• [bug]: Channel not propagating in gossip and unable to update policies #7973 — More detailed report: a newly opened channel (24hrs) doesn't appear on anyone's graph and updatechanpolicy returns "channel from self node has no policy". Also shows FeeReport failing with "no policy for outgoing channel". Includes full channel details showing the channel is active with ChanStatusDefault, commitment type ANCHORS, but zero num_updates.

[yyforyongyu]

Can you search your logs for patterns like Attempt to add missing edge for ?

I think this specific area is becoming spaghetti,

lnd/routing/localchans/manager.go

Lines 200 to 218 in 344af33

	case createMissingEdge:
	log.Warnf("Missing edge for active channel (%s) "+
	"during policy update. Recreating edge with "+
	"default policy.",
	channel.FundingOutpoint.String())
	info, edge, failedUpdate := r.createMissingEdge(
	ctx, channel, newSchema,
	)
	if failedUpdate == nil {
	err = processChan(info, edge)
	if err != nil {
	return nil, err
	}
	} else {
	failedUpdates = append(
	failedUpdates, failedUpdate,
	)
	}

To make this cli better, we should create a new command addmissingedge instead, check that the edge is indeed missing, then create it, keep it simple.

And we should properly fix it by investigating the root cause of the missing edge - the create_missing_edge was a bandage fix anyway.

[jogc]

Thanks for looking into this!
Yeah I got one of those while trying to recreate the edge:

[ERR] LCHN: Attempt to add missing edge for channel (<RELEVANT_CHANNEL_POINT>) errored with: expected the funding transaction script to be set

(grepped all logs I got and only found that one, actual channel point censored for privacy)

All messages I have gotten and what I have done are detailed here:
#10567